This invention relates to master cylinders and more particularly to master cylinders especially suited for use in a master/slave hydraulic control system.
Master cylinders are in common usage such, for example, as in combination with a slave cylinder to provide the actuating mechanism for a mechanical clutch of a motor vehicle.
A typical master cylinder assembly includes a casing structure defining a cylindrical bore and a piston slidably mounted in the bore. Pressurized hydraulic fluid is discharged from the cylindrical bore for delivery to the slave cylinder in response to stroking reciprocal movement of the piston in the bore. Effective operation of the cylinder assembly requires the establishment of an effective seal between the piston and the bore of the cylinder. This seal may either be mounted in an external groove in the piston or in an internal groove in the cylindrical wall defining the bore. In assemblies utilizing an internal groove in the cylindrical wall defining the bore, the groove defines a forward bore portion forwardly of the groove and a rearward bore portion rearwardly of the groove in which the piston is received in its retracted position. The forward end of the piston in the retracted position of the piston is typically proximate the groove but rearwardly of the forward bore portion to allow flow of recuperative fluid from the associated reservoir to a position forwardly of the piston as the piston retreats from an extended position to its retracted position whereby to ensure that the bore forwardly of the piston remains full at all times. This arrangement has the disadvantage that the front end of the piston is unsupported as the piston begins its forward stroke and remains unsupported until the piston moves through a transient region and enters the forward bore portion. During movement of the piston through the transient region, the piston may assume an angled disposition relative to the center line of the cylinder with resultant potential leakage conditions.
This invention relates to an improved master cylinder for use in a master cylinder/slave cylinder assembly.
More particularly, this invention relates to a master cylinder mounting the seal in an internal groove in the cylinder and yet providing total support for the piston throughout its stroke.
The master cylinder of the invention is of the type comprising a casing defining a bore and a piston mounted in the bore for stroking movement between rearwardly retracted and forwardly extended positions. The casing further defines an annular groove surrounding the bore between forward and rearward ends of the bore and defining a forward bore portion forwardly of the groove and a rearward bore portion rearwardly of the groove, and further defines a port connecting the annular groove with a reservoir for containing hydraulic fluid. A seal assembly is positioned in the groove.
According to the invention, the piston has a forward end positioned forwardly of the groove in a rearward section of the forward bore portion with the piston in its retracted position whereby, in its retracted position, a rear end of the piston is guided in the rearward bore portion and the forward end of the piston is guided in the rearward section of the forward bore portion, and axial groove means are provided at the interface between the forward end of the piston and the rearward section of the forward bore portion establishing communication, with the piston in its retracted position, between the bore forwardly of the piston and the annular groove. This arrangement allows the piston to be totally supported in the bore at all times and yet retains the ability to deliver recuperative fluid forwardly of the piston as the piston retreats toward its retracted position.
According to a further feature of the invention, the groove means comprises a series of circumferentially spaced, axially extending grooves in the rearward section of the forward bore portion. This arrangement provides an efficient means of delivering recuperative fluid forwardly of the retreating piston.
According to a further feature of the invention, the axial grooves extend into the forward bore portion forwardly of the rearward section of the forward bore portion and, in the disclosed embodiment, the axial grooves are substantially coextensive with the forward bore portion. This specific groove configuration ensures adequate recuperative flow irrespective of the extended forward position of the piston prior to retreating toward its retracted position.
According to a further feature of the invention, the casing defines an annular shoulder defining a forward end of the annular groove and an annular lip projecting rearwardly from the shoulder into the annular groove; the seal assembly includes an annular seal positioned in the annular groove against the annular lip; the annular lip is crenellated and coacts with the seal to define a plurality of circumferentially spaced crenel passages therebetween providing fluid communication between the reservoir port and the axial grooves; and the seal includes an outer flexible lip movable in response to variations in fluid pressure between an outwardly flexed position blocking fluid communication between the reservoir port and the crenel passages and an inwardly flexed position allowing fluid communication between the reservoir port and the crenel passages and thereby between the reservoir port and the axial grooves. This arrangement selectively allows flow of recuperative fluid into the forward portion of the bore ahead of the retreating piston.
According to a further feature of the invention, the casing comprises a two-part structure including a molded front part and a molded rear part; and the front and rear parts include coacting means for joining the parts in a configuration in which the front part defines the forward bore portion and the axial grooves, the rear part defines the rearward bore portion, and the parts coact to define the annular groove. This specific construction provides a ready and inexpensive means of constructing the master cylinder assembly.
According to a further feature of the invention, the annular shoulder comprises a forward annular shoulder; the annular groove is further defined by a rearward annular shoulder defining a rearward end of the groove and a cylindrical groove surface interconnecting the forward and rearward annular shoulders; and in the joined configuration of the front and rear parts the forward annular shoulder, the annular lip, the reservoir port, and the cylindrical groove surface are defined by the front part and the rear annular shoulder is defined by the rear part. This specific part configuration allows the master cylinder to be readily assembled with a telescopic movement.
According to a further feature of the invention, the annular seal comprises a primary seal, and the master cylinder further includes a secondary annular seal positioned in the annular groove against the rearward annular shoulder, rearwardly of the primary seal, and rearwardly of the reservoir port. This arrangement allows the use of primary and secondary seals to minimize leakage between the piston and the bore.
According to a further feature of the invention, the master cylinder further includes an annular spacer positioned in the annular groove between the primary seal and the secondary seal proximate the reservoir port, and the spacer provides passage means allowing the passage of fluid therethrough. This arrangement allows the spacer to maintain the primary and secondary seals in their defined positions and further allows the ready flow of recuperative fluid into the area in the bore ahead of the retreating piston.
Other applications of the present invention will become apparent to those skilled in the art when the following description of the best mode contemplated for practicing the invention is read in conjunction with the accompanying drawings.